Preparation of emulsions by pH adjustments

ABSTRACT

The present invention provides a water-in-oil explosive emulsion comprised of a continuous oil phase; a discontinuous aqueous phase containing a functional component and an emulsifying amount of a hydrocarbyl-substituted carboxylic acid or anhydride or ester or another derivation of said acid or anhydride; where the pH of the aqueous phase has been adjusted to a pH of at least 6.0 by the addition of a base other than the functional component. It has been discovered that the adjustment of the pH of the aqueous phase to a pH of at least 6.0 results in a considerably stable emulsion, even when the hydrocarbyl-substituted emulsifier is not aminated. A further stabilization of the emulsion can be accomplished through the use of sensitizing agents such as microspheres in order to ease handling and repumping of the explosive emulsion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a water-in-oil emulsion explosive and a method of preparing same. More particularly, the present invention relates to emulsion explosives containing a PIBSA-based emulsifier in a pH adjusted environment.

[0003] 2. Description of the Related Art

[0004] Water-in-oil emulsion explosives are well-known in the art, see, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives are found to have certain advantages over conventional aqueous slurry explosives, which have a continuous aqueous phase, as described in U.S. Pat. No. 4,141,767.

[0005] An inherent problem with emulsion explosives, however, is their relative instability, due to the act that they comprise a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable these supercooled droplets are prevented from crystallizing or solidifying into a lower energy state. If the emulsion weakens or becomes unstable, however, then crystallization or solidification of the droplets results, and the explosive generally loses at least some of its sensitivity to detonation and becomes too viscous to handle for certain blasting applications. Moreover, it is common to add solid components to emulsion explosives, such as glass microspheres for density reduction and prills or particles of oxidizer salt such as porous prilled ammonium nitrate (AN) for increased energy. These solid components, however, tend to destabilize emulsions.

[0006] Emulsion explosives commonly are used as a repumpable explosive, i.e., an explosive that is formulated at a remote facility, loaded or pumped into a bulk container and then transported in the container to a blasting site where it then is “repumped” from the container into a borehole. Alternatively, the explosive may be delivered (repumped) into a centrally located storage tank from which it will be further repumped into a vehicle for transportation to a blasting site and then again repumped into the borehole. Thus the emulsion explosive must remain stable even after being subjected to repeated handling or searing action, which normally also tends to destabilize an emulsion. Additionally, the emulsion's viscosity must remain low enough to allow for repumping at reasonable pressures and at the low ambient temperatures that may be experienced during colder months. Repeated handling or hearing action also tends to increase the emulsion's viscosity.

[0007] Since a density control agent is required in many instances to reduce the density of an explosive and thereby increase its sensitivity to a required level for detonation, and since hollow microspheres are a preferred form of density control, it is important that the emulsion remain stable and have a low viscosity even when containing solid density control agents.

[0008] Proposals have been made to improve the stability of water-in-oil emulsion explosives by employing particular surfactants which function to a high level of efficiency in the harsh environment of an oxidizer salt solution. A particularly effective and useful surfactant has been the reaction product of a hydrocarbyl-substituted succinic acid or anhydride and an amine.

[0009] For example, U.S. Pat. No. 4,708,753 discloses water-in-oil emulsions containing as the emulsifier a salt derived from a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or amide derivative thereof, and an amine.

[0010] U.S. Pat. No. 4,615,751 discloses the use of an unspecified polybutenyl succinic anhydride derivative (with a tradename of EXPERSE 60) as a water-resisting agent in emulsions containing prills but not as an emulsifier. European Patent Application No. 0 155 800 discloses alkanolamine derivatives of polyisobutenyl succinic anhydride (PIBSA) as emulsifiers. See also U.S. Pat. Nos. 4,822,433; 4,919,179 also describes a PIBSA-based surfactant for use in explosive emulsions.

[0011] U.S. Pat. No. 4,710,248 discloses water-in-oil emulsion explosives containing as an emulsifier underivatized polyisobutenyl succinic anhydride or polyisobutenyl succinic acid.

[0012] U.S. Pat. No. 4,357,184 discloses water-in-oil emulsions containing graft block or branched polymer emulsifiers. One type of block copolymer which is taught contains polyisobutenyl succinic anhydride as the hydrophobic block and polyethylene glycol or polyethylenimine as the hydrophillic block.

[0013] The use of amines in preparing emulsifiers for use in explosive emulsions, however, can be expensive. Avoiding the use of amines in the amination of a hydrocarbyl-substituted compound, therefore, would be economically beneficial provided the stability, among other properties, of the emulsion are not sacrificed.

[0014] It is an object of the present invention, therefore, to provide such an explosive emulsion where the emulsifier employs only a hydrocarbyl-substitute compound, and can avoid the use of expensive amines.

SUMMARY OF THE INVENTION

[0015] The present invention provides a water-in-oil explosive emulsion comprised of a continuous oil phase; a discontinuous aqueous phase containing a functional component and an emulsifying amount of a hydrocarbyl-substituted carboxylic acid or anhydride or ester or another derivation of said acid or anhydride; where the pH of the aqueous phase has been adjusted to a pH of at least 6.0 by the addition of a base other than the functional component. It has been discovered that the adjustment of the pH to a pH of at least 6.0 results in a considerably stable emulsion, even when the hydrocarbyl-substituted emulsifier is not aminated. A further stabilization of the emulsion can be accomplished through the use of sensitizing agents such as microspheres in order to ease handling and repumping of the explosive emulsion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The hydrocarbyl-substituted carboxylic acids, and anhydrides, and ester and amide derivatives thereof, can be prepared by any of several known procedures which are described in the following U.S., British and Canadian patents: U.S. Pat. Nos. 3,024,237; 3,087,936; 3,172,982; 3,215,707; 3,219,666; 3,231,587; 3,245,910; 3,254,025; 3,271,310; 3,272,743; 3,272,746; 3,278,550; 3,288,714; 3,307,928; 3,312,619; 3,341,542; 3,367,943; 3,373,111; 3,374,174; 3,381,022; 3,394,179; 3,454,607; 3,346,354; 3,470,098; 3,630,902; 3,652,616; 3,755,169; 3,868,330; 3,912,764; and 4,368,113. British Patent Nos. 944,136; 1,085,903; 1,162,436; and 1,440,219. Canadian Patent No. 956,397. These patents are incorporated herein by reference.

[0017] The olefinic monomers of C₄ through C₁₈ may be used singly or in combination. However, the average chain length of the olefinic or vinyl addition polymer (excluding branching or side chains) should be within the range of 10 to 32 carbon atoms. The olefinic or vinyl addition polymers are conveniently bis-carboxylated or converted to an acid anhydride derivative by reaction with such materials as succinic or maleic anhydride, succinic maleic acid, tetrahydrophthalic anhydride, mesaconic acid, glutaconic acid, sorbic acid, itaconic acid, itaconic anhydride and the like.

[0018] The oxygen-supplying component or functional component of the discontinuous phase suitably comprises any oxidizer salt capable of releasing oxygen in an explosive environment in an amount and at a rate sufficient to confer acceptable explosive characteristics on the emulsion composition. Inorganic oxidizer salts conventionally employed in the production of emulsion explosive compositions, and suitable for inclusion in the compositions of the present invention, are disclosed, for example, in U.S. Pat. No. 3,447,978. This include ammonium salts and salts of the alkali- and alkaline-earth metals—such as the nitrate, chlorate and perchlorate salts, and mixtures thereof. Other suitable salts include hydrazine nitrate and urea perchlorate. The oxygen-supplying component may also comprise an acid, such as nitric acid.

[0019] Ammonium nitrate is preferably employed as a primary oxidizer salt. From about 10% to about 65% of the total oxidizer salt for an explosive composition may be added in particle or prill form. For example, AN prills or ANFO can be combined with and mixed into the emulsion to form an explosive composition. A particular advantage of the present invention is improved emulsion stability in the presence of such prills.

[0020] The pH of this discontinuous phase is altered by the addition of a base other than the original functional component. In preferred embodiments, the types of bases that can be used are ammonium hydroxide, calcium hydroxide, sodium hydroxide, and potassium hydroxide. The pH of the discontinuous phase must be at least 6.0, the minimum pH in which polyisobutenyl succinic anhydride will perform adequately. More preferably, the pH of the aqueous phase is in the range of from 6.0 to 8.0, even more preferably in the range of from 6.0 to 7.0, and most preferably in the range of from 6.0 to 6.2. By increasing the pH from that typically used, the blend stability of the emulsions of the present invention have been found to be much improved. The formulations of the present invention also lowers viscosity and promotes pumpability. Though amines can be used for pH adjustment, the use of aqueous bases will be more cost effective. Thus, through pH adjustment and not the use of amines, the emulsions are stable and can be produced saving both time and money.

[0021] The organic medium capable of forming the continuous phase of an emulsion explosive composition in accordance with the invention serves as a fuel for the explosive composition and should be substantially insoluble in the component(s) of the discontinuous phase with which it should be capable of forming an emulsion in the presence of an effective amount of an appropriate emulsifying agent. Ease of emulsification depends, inter alia, on the viscosity of the organic medium and although the resultant emulsion may have a substantially solid continuous phase, the organic medium should be capable of existing initially in a sufficiently fluid state, if necessary, in response to appropriate temperature adjustment, to permit emulsification to proceed.

[0022] Suitable organic media which are capable of existing in the liquid state at convenient emulsion formulation temperatures include saturated and unsaturated aliphatic and aromatic hydrocarbons, and mixtures thereof. Preferred media include refined (white) mineral oil, diesel oil, paraffin oil, petroleum distillates, benzene, toluene, dinitrotoluene, styrene, xylenes, and mixtures thereof.

[0023] In addition to the organic fuel medium, the continuous phase may optionally comprise a wax to control the rheology of the system, although the presence of a wax is not necessary to achieve the desired conductivity levels. Suitable waxes include petroleum, mineral, animal, and insect waxes. The preferred waxes have melting temperatures of at least 30° C. and are readily compatible with the formed emulsion. A preferred wax has a melting temperature in a range of from about 40° C. to 75° C.

[0024] Generally, the continuous phase (including wax(es), if present) comprises from 1 to 10, and preferably from 2 to 8% by weight of the total explosive composition, but higher proportions, for example in a range of from 1 up to 15 or even 20% may be tolerated.

[0025] When the inventive emulsions are employed as explosive emulsions, such emulsions typically contain other additional additives such as sensitizing components, oxygen-supplying salts, particulate light metals, particulate solid explosives, soluble and partly soluble self-explosives, explosive oils and the like for purposes of augmenting the strength and sensitivity or decreasing the cost of the emulsion.

[0026] The sensitizing components are distributed substantially homogeneously throughout the emulsions. These sensitizing components are preferably occluded gas bubbles which may be introduced in the form of glass or resin microspheres or other gas-containing particulate materials. Alternatively, gas bubbles may be generated in-situ by adding to the composition and distributing therein a gas-generating material such as, for example, an aqueous solution of sodium nitrite. Other suitable sensitizing components which may be employed alone or in addition to the occluded or in-situ generated gas bubbles include insoluble particulate solid self-explosives such as, for example, grained or flaked TNT, DNT, RDX and the like and water-soluble and/or hydrocarbon-soluble organic sensitizers such as, for example, amine nitrates, alkanolamine nitrates, hydroxyalkyl nitrates, and the like. The explosive emulsions of the present invention may be formulated for a wide range of applications. Any combination of sensitizing components may be selected in order to provide an explosive composition of virtually any desired density, weight-strength or critical diameter.

[0027] The quantity of solid self-explosive ingredients and of water-soluble and/or hydrocarbon-soluble organic sensitizers may comprise up to about 40% by weight of the total emulsion. The volume of the occluded gas component may comprise up to about 50% of the volume of the total explosive emulsion.

[0028] Optional additional materials may be incorporated in the explosive emulsions of the invention in order to further improve sensitivity, density, strength, rheology and cost of the final explosive. Typical of materials found useful as optional additives include, for example, emulsion promotion agents such as highly chlorinated paraffinic hydrocarbons, particulate oxygen-supplying salts such as prilled ammonium nitrate, calcium nitrate, perchlorates, and the like, particulate metal fuels such as aluminum, silicon and the like, particulate non-metal fuels such as sulfur, gilsonite and the like, particulate inert materials such as sodium chloride, barium sulphate and the like, water phase or hydrocarbon phase thickeners such as guar gum, polyacrylamide, carboxymethyl or ethyl cellulose, biopolymers, starches, elastomeric materials, and the like, crosslinkers for the thickeners such as potassium pyroantimonate and the like, buffers or pH controllers such as sodium borate, zinc nitrate and the like, crystals habit modifiers such as alkyl naphthalene sodium sulphonate and the like, liquid phase extenders such as formamide, ethylene glycol and the like and bulking agents and additives of common use in the explosives art.

[0029] The quantities of optional additional materials used may comprise up to about 50% by weight of the total explosive composition, the actual quantities employed depending upon their nature and function.

[0030] Preparing the water-in-oil emulsion in accordance with the present invention comprises first preparing a continuous oil phase, and preparing a discontinuous aqueous phase having a functional component therein. The pH of the aqueous phase is adjusted by the addition of a base other than the functional component. The additional base can comprise, for example, ammonium hydroxide, calcium hydroxide, potassium hydroxide, sodium hydroxide or ammonia. The pH to which the aqueous phase is adjusted is to a pH level of at least 6.0, and most preferably in the range of from 6.0 to 6.2, which is higher than the typical range of from 4.0 to 5.5. The aqueous phase is then emulsified into the continuous oil phase using an emulsifying amount of a hydrocarbon-substituted carboxylic acid, an anhydride, ester or derivative of said ester or anhydride.

[0031] The following examples are provided to further illustrate the present invention and the advantages thereof, and are not meant to be limiting in any way.

EXAMPLE 1

[0032] Twelve different PIBSA-based emulsions were made. Some had pH adjustments made to the aqueous phase, other did not. A continuous phase of oil and emulsifier was blended with an ammonium nitrate solution by pouring the ammonium nitrate solution into the oil blend and stirring in a mixer to effect emulsification. The stability of each of the emulsions, as well as the viscosity and particle size were observed.

[0033] Emulsion 1 was a polyisobutenyl succinic anhydride emulsion made with no pH adjustment of the aqueous phase. It made a fairly good emulsion but blend stability was compromised. The viscosity and particle size of this emulsion were higher than the others, also, which is characteristic of polyisobutenyl succinic anhydride.

[0034] Emulsions 2-10 involved the use of polyisobutenyl succinic anhydride, but pH adjustments were made to the aqueous phase using amines and common aqueous bases. All pH measurements were in the 6-7 range. This is the minimum pH in which polyisobutenyl succinic anhydride will perform adequately. The blend stability of these emulsions was much improved and all blend samples remained in perfect condition. A beneficial decrease in product viscosities and particle size was observed. The increase in ANFO blend stability is of particular commercial importance since a great deal of product blended with ANFO is sold and these formulations are adequate as long as pH is monitored. The present invention therefore provides a very economical alternative to the prior art.

[0035] The use of these formulations is ideally suited to an all emulsion product as they have lower viscosities to promote pumpability. The elimination of the amination reactions currently used for commercial PIBSA-based emulsifiers saves both time and money. Though amines can be used for pH adjustment, the use of aqueous bases will be more cost effective.

[0036] The formulations of emulsions 11 and 12 were made to show the negative effect that acidic pH has on polyisobutenyl succinic anhydride emulsions. The low pH (about 5.0) causes instability in blends and the addition of glass microspheres produces immediate separation and crystallization of the emulsion. These tests demonstrate that pH is a controlling factor in the stability of a hydrocarbyl-substituted acid or anhydride emulsion.

[0037] Based upon the foregoing, it can be concluded that a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or another derivation of said acid or anhydride, and in particular polyisobutenyl succinic anhydride, is an adequate emulsifier when the pH of the aqueous phase is monitored and adjusted correctly.

EXAMPLE 2

[0038] Eight emulsions were prepared using neat polyisobutenyl succinic anhydride (Runs 1-8) following the procedure of Example 1. The pH of the discontinuous aqueous phase was adjusted to acidic or basic pH using various agents, as shown in the Table below.

[0039] Six additional emulsions were prepared using a commercial aminated polyisobutenyl succinic anhydride product under the same basic pH conditions in which the neat polyisobutenyl succinic anhydride emulsions were made. (Runs A-F). The pH of the emulsion aqueous phase in Runs C-F was adjusted to between 6.9 and 7.0 with ammonium hydroxide, calcium hydroxide, sodium hydroxide and potassium hydroxide. The interesting result is that experiment D (calcium hydroxide) was disastrous for the commercial aminated emulsifier. The neat polyisobutenyl succinic anhydride emulsifier (experiment 5) handled the same conditions beautifully and all samples retained are still in excellent condition with no signs of emulsion breakage. This is an improvement over the traditional aminated polyisobutenyl succinic anhydride emulsifier.

[0040] The stability of each emulsion, as well as the viscosity and particle size were observed. A paint shaker test was also used to test the viscosity and particle size. The test involved filling a paint can approximately halfway with emulsion, sealing the can and shaking the can for about four continuous hours in an electronic paint shaker. After allowing the emulsion in the can to come to ambient temperature once the shaking has stopped, the emulsion was measured for density, viscosity and particle size. All results are shown in the Table below. TABLE Paint Microsphere Freeze/Thaw Paint Paint Shaker Emulsifier Run Base/Acid (pH) Viscosity Particle 50/50 Blend Sample Shelf- Passed Shaker Shaker Particle Used No. Used Reading @ ambient Size Shelf-Life*** Life*** (2 cycles) Passed Viscosity Size PIBSA* 1 HNO₃ 2.3 23000 17.11 1 day Broken Yes Yes 32000 13.27 PIBSA* 2 None 5.4 34000 15.35 1 week Excellent Yes Yes 31000 13.28 PIBSA* 3 NaOH 6.98 21000 13.25 Excellent Excellent Yes Yes 24000 12.98 PIBSA* 4 KOH 6.9 17000 15.69 Excellent Excellent Yes Yes 20000 13.27 PIBSA* 5 Ca(OH)₂ 6.92 20000 12.9 Excellent Excellent Yes Yes 24000 11.99 PIBSA* 6 TEA 6.95 19000 14.63 Excellent Excellent Yes Yes 29000 11.11 PIBSA* 7 DEA 6.98 19000 13.27 Excellent Excellent Yes Yes 25000 11.52 PIBSA* 8 DEEA 6.95 27000 10.12 Excellent Excellent Yes Yes 28000 9.58 A-PIBSA** A HNO₃ 2.2 34000 6.96 Excellent Excellent Yes Yes 32000 6.39 A-PIBSA** B None 5.2 33000 6.67 Excellent Excellent Yes Yes 45000 4.43 A-PIBSA** C NH₃OH 6.95 27000 7.21 Ongoing**** Ongoing**** Yes Yes 31000 4.94 A-PIBSA** D Ca(OH)₂ 6.5 (crystals) 14.02 24 hours Broken No No Separation & Crystallization A-PIBSA** E NaOH 6.6 24000 6.49 Ongoing**** Ongoing**** Yes Yes 34000 5.41 A-PIBSA** F KOH 6.6 23000 7.61 Ongoing**** Ongoing**** Yes Yes 40000 4.16

[0041] While the present invention has been described in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention described herein is intended to cover such modifications as fall within the scope of the claims appended hereto. 

What is claimed is:
 1. A water-in-oil emulsion comprising: a continuous oil phase; a discontinuous aqueous phase containing a functional component; and an emulsifying amount of a hydrocarbyl-substituted carboxylic acid or anhydride or ester or derivative of said acid or anhydride; where the pH of the aqueous phase has been adjusted to a pH of at least 6.0 by the addition of a base other than the functional component.
 2. The water-in-oil emulsion of claim 1, wherein the hydrocarbyl-substituted compound is an anhydride.
 3. The water-in-oil emulsion of claim 2, wherein the anhydride is polyisobutenyl succinic anhydride.
 4. The water-in-oil emulsion of claim 1, wherein the hydrocarbyl-substituted compound is aminated.
 5. The water-in-oil emulsion of claim 1, wherein the base used to adjust the pH is comprised of ammonium hydroxide, calcium hydroxide, potassium hydroxide, sodium hydroxide, or ammonia.
 6. The water-in-oil emulsion of claim 1, wherein the adjusted pH level is in the range from 6.0-8.0.
 7. The water-in-oil emulsion of claim 1, wherein the adjusted pH is in the range of from 6.0-7.0.
 8. The water-in-oil emulsion of claim 1, wherein the adjusted pH is in the range of from 6.0-6.2.
 9. The water-in-oil emulsion of claim 1, wherein the functional component is ammonium nitrate.
 10. The explosive emulsion of claim 1, wherein the emulsion is further sensitized.
 11. The explosive emulsion of claim 10, wherein the emulsion comprises microspheres.
 12. A method for preparing a water-in-oil emulsion comprising a continuous oil phase and a discontinuous aqueous phase which comprises: preparing a continuous oil phase; preparing a discontinuous aqueous phase having a functional component therein, adjusting the pH of the aqueous phase by the addition of a base other than the functional component; and emulsifying the aqueous phase into the continuous oil phase using an emulsifying amount of a hydrocarbyl-substituted carboxylic acid or anhydride or ester or derivative of said acid or anhydride.
 13. The method of claim 12, wherein the hydrocarbyl-substituted compound is an anhydride.
 14. The method of claim 13, wherein the anhydride is polyisobutylene succinic anhydride.
 15. The method of claim 12, wherein the hydrocarbyl-substituted compound is aminated.
 16. The water-in-oil emulsion of claim 12, wherein the base used to adjust the pH is ammonium hydroxide, calcium hydroxide, potassium hydroxide, sodium hydroxide, or ammonia.
 17. The water-in-oil emulsion of claim 16, where in the pH adjustment is to a pH level of at least 6.0.
 18. The method of claim 17, wherein the pH adjustment is to a pH in the range of from 6.0 to 8.0.
 19. The method of claim 17, wherein the pH adjustment is to a pH in the range of from 6.0 to 7.0.
 20. The method of claim 17, wherein the pH adjustment is to a pH in the range of from 6.0 to 6.2.
 21. The method of claim 12, wherein the aqueous phase comprises ammonium nitrate as an oxidizer salt.
 22. The method of claim 12, wherein a sensitizing component is mixed into the emulsion.
 23. The method of claim 23, wherein the sensitizing component comprises microspheres. 